1) Manufacturers of portable chargers lie about the rated capacity of their products. Don't believe you're getting 5v or 2a just because the box says you are.
2) Most USB cables are inadequate at delivering the necessary power to the Stratux due to severe voltage drop over their flimsy wires. Buy a known, good quality cable. A sufficient power supply with an insufficient cable will cause problems, and vice versa. The Pi will automatically shunt power to peripherals (SDR's, GPS, etc.) if it detects low voltage, so insufficient power issues usually are hidden within "my radio's don't work!" type problems. The red light on the Pi means voltage is good. There's a kid in a Stratux forum who is adamant that his Pi is getting sufficient power because he's using a wall charger. His red light is not on. Some people can't be helped.
3) There's no such thing as a 5v battery. Portable "chargers" are full of 3.7v batteries that are connected together and bucked up to 5v. The charger rating, i.e. "10AH", is the total rating of the 3.7v batteries before the overhead of bucking it up to 5v is considered. Bucking costs a minimum of 10%, sometimes 20%. So your "10AH" battery is really capable of providing 8-9AH. But wait, that's not all! Battery industry specs allow these batteries to lose up to 20% of their charge volume and still maintain their inflated rating, so after a few months of use your "10AH" charger is now capable of giving you maybe 70% of the rated capacity and still be within spec.
So the trick to keeping your Stratux happy and powered up for the entire flight is to buy quality components and pad your numbers. Anker is a popular brand with Stratux users for chargers and cables, and there are a few other quality brands.